This application relates to optical detection of properties of a material or structure with a reflective surface.
An optical beam may be used as a probe to detect properties of various materials and structures that can interact with the optical beam. In particular, optical reflection of the optical probe beam from a reflective surface of a structure may be measured and processed to determine certain properties of that surface. For example, material parameters such as the optical absorption coefficient or the refractive index of the material that forms the surface may be measured from the optical reflection. Also, geometrical parameters of the surface, such as the thickness of a thin film that is at least partially transparent, or the curvature of the reflective surface, may be measured from the optical reflection.
Optical detection may achieve certain advantages. For example, when the power of the probe beam can be kept at a sufficiently low power level, the optical detection can be non destructive or evasive so that the properties of the measured object may be preserved. The probe beam may also be expanded to illuminate an area of a target object so that each location in the entire illuminated area may be measured at the same time. Optical detection may also be used to achieve full-field measurements at high speeds or with high accuracy.
This application includes techniques and systems that integrate an optical coherent gradient sensing (CGS) module and another optical sensing module such as an optical ellipsometer to use a single probe beam to simultaneously measure properties of a specularly reflective surface. A collimated coherent optical probe beam is used to illuminate a target area on the reflective surface to obtain information on each location within the illuminated target area for measurements of both the ellipsometer and the CGS module. The reflected beam is split into a first part for the ellipsometry measurements and a second part for the CGS measurements. The ellipsometer operates to determine the optical properties of the sample. For example, refractive indices, the absorption coefficient of a thin film formed on a substrate, or the thickness of the thin film, among others, may be determined. The CGS module operates to determine the surface curvature of each location of the illuminated area. Notably, the material properties and the surface curvature of each location within the illuminated area are measured at the same location and time by extracting information from the same reflected beam from the surface under measurement. Measurements at different locations within the illuminated area are made at the same time.